Non-aqueous electrolyte and electrochemical device comprising the same

ABSTRACT

Disclosed is a non-aqueous electrolyte comprising: an acrylate compound; a sulfinyl group-containing compound; an organic solvent; and an electrolyte salt. Also, disclosed is an electrode comprising a coating layer formed partially or totally on a surface thereof, the coating layer comprising: (i) a reduced form of an acrylate compound; and (ii) a reduced form of a sulfinyl group-containing compound. Further, disclosed is an electrochemical device comprising a cathode, an anode and a non-aqueous electrolyte, wherein (i) the non-aqueous electrolyte is the aforementioned non-aqueous electrolyte; and/or (ii) the cathode and/or the anode is the aforementioned electrode.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a national phase entry under 35 U.S.C. §371of International Application No. PCT/KR2007/005125, filed Oct. 19, 2007,published in English, which claims the benefit of Korean PatentApplication No. 10-2006-0103934, filed Oct. 25, 2006. The disclosures ofsaid applications are incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a non-aqueous electrolyte, an electrodeand an electrochemical device comprising the same. More particularly,the present invention relates to a non-aqueous electrolyte comprisingcompounds capable of improving the lifespan and thermal stability of anelectrochemical device, and an electrochemical device comprising thesame. Also, the present invention relates to an electrode comprisingreduced forms of compounds capable of improving the lifespan and thermalstability of an electrochemical device, and an electrochemical devicecomprising the same.

BACKGROUND ART

Recently, there has been increasing interest in energy storagetechnology. As batteries have been widely used as energy sources inportable phones, camcorders, notebook computers, PCs and electric cars,research and development of electrochemical devices have been madeintensively. In this regard, electrochemical devices are subjects ofgreat interest. Particularly, development of rechargeable secondarybatteries has been the focus of attention. More recently, research anddevelopment of an electrode and a battery having a novel design havebeen conducted in order to improve capacity density and specific energythereof.

Among the currently used secondary batteries, lithium secondarybatteries, developed in early 1990's, have drive voltage and energydensity higher than those of conventional batteries using aqueouselectrolytes (such as Ni-MH batteries, Ni—Cd batteries and H₂SO₄—Pbbatteries), and thus are spotlighted in the field of secondarybatteries. However, a lithium secondary battery has a problem in that itundergoes degradation of quality during repeated charge/dischargecycles. Such problems become more serious as the capacity density of thebattery increases.

Therefore, there is a continuous need to develop a means for improvinglifespan of a secondary battery.

Japanese Laid-Open Patent No. 2002-158034 discloses an acrylic compoundas an additive for an electrolyte, the acrylic compound being able toinhibit gas generation in a lithium secondary battery and deteriorationof an anode. Additionally, Japanese Laid-Open Patent No. 2003-168479discloses that the use of an acrylic compound having at least threeacryl groups as an additive for an electrolyte in a lithium secondarybattery leads to formation of a solid electrolyte interface (SEI) layervia reduction at an anode, and such SEI layers inhibit decomposition ofthe electrolyte at the anode so as to improve lifespan characteristicsof the battery.

DISCLOSURE OF INVENTION Technical Problem

Therefore, the present invention has been made in view of theabove-mentioned problems. In general, when an acrylate compound having apolymerizable double bond is used as an additive for an electrolyte inan electrochemical device, such as a lithium secondary battery, it isreduced at the anode of the battery in advance of the main solvent, suchas ethylene carbonate, to form a solid electrolyte interface (SEI) layerwith excellent quality. In this regard, the inventors of the presentinvention have found that when a sulfinyl group-containing compound isused in combination with the acrylate compound, the aforementionedeffect provided by the acrylate compound can be maximized.

Therefore, it is an object of the present invention to provide anon-aqueous electrolyte that comprises an acrylate compound incombination with a sulfinyl group-containing compound, and anelectrochemical device comprising the above non-aqueous electrolyte.

Technical Solution

In order to achieve the above-mentioned object, there is provided anon-aqueous electrolyte comprising: an acrylate compound; a sulfinylgroup-containing compound; an organic solvent; and an electrolyte salt.

Also, there is provided an electrode comprising a coating layer formedpartially or totally on a surface thereof, the coating layer comprising:(i) a reduced form of an acrylate compound; and (ii) a reduced form of asulfinyl group-containing compound.

Further, there is provided an electrochemical device comprising acathode, an anode and a non-aqueous electrolyte, wherein (i) thenon-aqueous electrolyte is the aforementioned non-aqueous electrolyteaccording to the present invention; and/or (ii) the cathode and/or theanode is the aforementioned electrode according to the presentinvention.

Mode for the Invention

The non-aqueous electrolyte according to the present invention ischaracterized by comprising an acrylate compound in combination with asulfinyl group-containing compound. It is known that when an acrylatecompound having a polymerizable double bond is used as an additive foran electrolyte in an electrochemical device, the acrylate compound isreduced at the anode in advance of a carbonate solvent used as the mainsolvent to form a solid electrolyte interface (SEI) layer with excellentquality. The effect provided by the acrylate compound can be maximizedwhen a sulfinyl group-containing compound is used in combination withthe acrylate compound.

When the acrylate compound is reduced, it forms a relatively thick anddense SEI layer, while the sulfinyl group-containing compound forms arelatively thin and porous SEI layer. Due to such different densities,when the above compounds are used in combination as additives for anelectrolyte according to the present invention, a first SEI layer isformed by one component, and then a second SEI layer may be formed bythe other component on a thinner or porous portion of the first SEIlayer or on a portion of the anode surface having no SEI layer. As aresult, a firm SEI layer can be formed on the anode surface. Therefore,it is possible to improve the quality of an electrochemical device byusing the non-aqueous electrolyte comprising the acrylate compound incombination with the sulfinyl group-containing compound formanufacturing the electrochemical device.

In the non-aqueous electrolyte according to the present invention, theacrylate compound includes a compound having one or more acryl groups inits molecule. Non-limiting examples of such acrylate compounds include,but are not limited to: tetraethyleneglycol diacrylate,polyethyleneglycol diacrylate (molecular weight 50˜20,000), bisphenol Aethoxylated diacrylate (molecular weight 100˜10,000), 1,4-butanedioldiacrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate,trimethylolpropane ethyoxylate triacrylate, trimethylolpropanepropoxylate triacrylate, ditrimethylolpropane tetraacrylate,pentaerythritol tetraacrylate, pentaerythritol ethoxylate tetraacrylate,dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate,tris[2-(acryloyloxy)ethyl]isocyanurate, or the like. The above acrylatecompounds may be used alone or in combination.

The acrylate compound is used in an amount of 0.05˜10 wt % in thenon-aqueous electrolyte. When the acrylate compound is used in an amountless than 0.05 wt %, it is not possible to improve the lifespan of anelectrochemical device sufficiently despite the use of the acrylatecompound. When the acrylate compound is used in an amount greater than10 wt %, irreversible capacity increases, resulting in degradation ofthe quality of the electrochemical device using the same compound.

In the non-aqueous electrolyte according to the present invention,non-limiting examples of the sulfinyl group-containing compound includesulfites, sulfonates and sultones, and the above compounds may be usedalone or in combination.

The sulfite compound may be represented by the following Formula 1:

wherein each of R¹ and R² independently represents a hydrogen atom,halogen atom, C1˜C6 alkyl group, C6˜C12 aryl group, C2˜C6 alkenyl groupor a halogen derivative thereof, and R₁ and R₂ may be bound to eachother.

Particular examples of the sulfite include, but are not limited to:ethylene sulfite, methyl ethylene sulfite, ethyl ethylene sulfite,4,5-dimethyl ethylene sulfite, 4,5-diethyl ethylene sulfite, propylenesulfite, 4,5-dimethyl propylene sulfite, 4,5-diethyl propylene sulfite,4,6-dimethyl propylene sulfite, 4,6-diethyl propylene sulfite,1,3-butylene glycol sulfite, or the like. The above sulfite compoundsmay be used alone or in combination.

The sulfonate compound may be represented by the following Formula 2:

wherein each of R³ and R⁴ independently represents a hydrogen atom,halogen atom, C1˜C6 alkyl group, C6˜C12 aryl group, C2˜C6 alkenyl groupor a halogen derivative thereof.

Particular examples of the sulfonate include, but are not limited to:methyl methane-sulfonate, ethyl methanesulfonate, methylethanesulfonate, propyl methanesulfonate, methyl propanesulfonate, ethylpropanesulfonate, ethenyl methanesulfonate, propenyl methanesulfonate,ethenyl benzenesulfonate, propenyl propenesulfonate, propenylcyanoethanesulfonate, or the like. The above sulfonate compounds may beused alone or in combination.

The sultone compound may be represented by the following Formula 3and/or Formula 4:

wherein each of R^(5˜)R¹⁰ independently represents a hydrogen atom,halogen atom, C1˜C6 alkyl group, C6˜C12 aryl group, C2˜C6 alkenyl groupor a halogen derivative thereof; and n is an integer of 1˜3.

wherein each of R¹¹˜R¹⁴ independently represents a hydrogen atom,halogen atom, C1˜C6 alkyl group, C6˜C12 aryl group, C2˜C6 alkenyl groupor a halogen derivative thereof; and n is an integer of 1˜3.

Particular examples of the sultone represented by Formulae 3 and 4include, but are not limited to: 1,3-propane sultone, 1,4-butanesultone, 1,3-propene sultone, 1,4-butene sultone, 1-methyl-1,3-propenesultone and derivatives thereof. The above sultone compounds may be usedalone or in combination.

The sulfinyl group-containing compound is used preferably in an amountof 0.1˜5 wt % in the non-aqueous electrolyte. When the sulfinylgroup-containing compound is used in an amount less than 0.1 wt %, it isnot possible to improve the lifespan of an electrochemical devicesufficiently. When the sulfinyl group-containing compound is used in anamount greater than 5 wt %, it causes undesired gas generation and anincrease in the impedance.

The non-aqueous electrolyte comprises an organic solvent. There is noparticular limitation in the organic solvent, as long as the solvent isone currently used for a non-aqueous electrolyte. Particular examples ofthe solvent include cyclic carbonates, linear carbonates, lactones,ethers, esters, acetonitriles, lactams and/or ketones. Halogenderivatives of such solvents may also be used.

Particular examples of the cyclic carbonates include ethylene carbonate(EC), propylene carbonate (PC), butylene carbonate (BC), fluoroethylenecarbonate (FEC), or the like. Particular examples of the linearcarbonates include diethyl carbonate (DEC), dimethyl carbonate (DMC),dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propylcarbonate (MPC), or the like. Particular examples of the lactonesinclude gamma-butyrolactone (GBL) and those of ethers include dibutylether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane,1,2-dimethoxyethane, 1,2-diethoxyethane, or the like. Particularexamples of the esters include methyl formate, ethyl formate, propylformate, methyl acetate, ethyl acetate, propyl acetate, methylpropionate, ethyl propionate, butyl propionate, methyl pivalate, or thelike. Additionally, particular examples of the lactams includeN-methylpyrrolidone (NMP), or the like. Further, particular examples ofthe ketones include polymethylvinyl ketone. Halogen derivatives of theabove organic solvents may also be used. Such organic solvents may beused alone or in combination.

The non-aqueous electrolyte according to the present invention furthercomprises an electrolyte salt. There is no particular limitation in theelectrolyte salt, as long as the electrolyte salt is one currently usedfor a non-aqueous electrolyte.

Non-limiting examples of the electrolyte salt include salts formed by acombination of: (i) a cation selected from the group consisting of Li⁺,Na⁺ and K⁺; with (ii) an anion selected from the group consisting of PF₆⁻, BF₄ ⁻, Cl⁻, Br⁻, I⁻, ClO₄ ⁻, AsF₆ ⁻, CH₃CO₂ ⁻, CF₃SO₃ ⁻, N(CF₃SO₂)₂and C(CF₂SO₂)₃ ⁻. Such electrolyte salts may be used alone or incombination. Particularly, a lithium salt is preferred.

In another aspect of the present invention, the electrode according tothe present invention comprises a coating layer, such as a solidelectrolyte interface (SEI) layer, formed partially or totally on asurface of the electrode, the coating layer comprising: (i) a reducedform of an acrylate compound; and (ii) a reduced form of a sulfinylgroup-containing compound.

The coating layer, such as the SEI layer, may be formed upon the firstcharge or during the subsequent charge/discharge cycles of theelectrochemical device using the electrode. The electrode according tothe present invention may be obtained by reducing an electrodemanufactured according to a method generally known to those skilled inthe art, at least once, in the non-aqueous electrolyte comprising theacrylate compound and the sulfinyl group-containing compound. In avariant, the electrode according to the present invention may beobtained by inserting a porous separator between a cathode and an anode,manufactured according to a method generally known to those skilled inthe art, introducing the non-aqueous electrolyte comprising the acrylatecompound and the sulfinyl group-containing compound thereto, and bysubjecting the resultant cell to at least one charge cycle.

In the electrode according to the present invention, the reduced form ofthe acrylate compound and the reduced form of the sulfinylgroup-containing compound may be produced via the reductivedecomposition of the acrylate compound and the sulfinyl group-containingcompound, respectively. Additionally, in the electrode according to thepresent invention, non-limiting examples of the acrylate compound andthe sulfinyl group-containing compound are the same as those of theacrylate compound and the sulfinyl group-containing compound used in thenon-aqueous electrolyte according to the present invention.

In still another aspect of the present invention, the electrochemicaldevice according to the present invention comprises a cathode, an anodeand a non-aqueous electrolyte, wherein the non-aqueous electrolyte isthe aforementioned non-aqueous electrolyte according to the presentinvention.

In a variant, the electrochemical device according to the presentinvention comprises a cathode, an anode and a non-aqueous electrolyte,wherein the cathode and/or the anode are/is the aforementioned electrodeaccording to the present invention. Herein, the non-aqueous electrolytemay be the aforementioned non-aqueous electrolyte according to thepresent invention.

The electrochemical device according to the present invention includesall types of devices in which electrochemical reactions are performed.Particular examples of the electrochemical device include all types ofprimary batteries, secondary batteries, fuel cells, solar cells,capacitors, or the like. Among the secondary batteries, lithiumsecondary batteries, including lithium metal secondary batteries,lithium ion secondary batteries, lithium polymer secondary batteries orlithium ion polymer secondary batteries, are preferred.

The electrochemical device may be obtained by using a conventionalmethod known to those skilled in the art. For example, a porousseparator is inserted between a cathode and an anode to form anelectrode assembly, and then the non-aqueous electrolyte according tothe present invention is injected thereto.

The electrode used in the electrochemical device according to thepresent invention may be manufactured by a conventional method known toone skilled in the art. For example, an electrode active material may bemixed with a solvent, and optionally with a binder, a conductive agentand a dispersant, and the mixture is agitated to provide slurry. Then,the slurry is applied onto a metal collector, and the collector coatedwith the slurry is compressed and dried to provide an electrode.

The electrode active material includes a cathode active material or ananode active material.

Cathode active materials that may be used in the present inventioninclude: lithium transition metal composite oxides, such as LiM_(x)O_(y)(M=Co, Ni, Mn, Co_(a)Ni_(b)Mn_(c)) (e.g. lithium manganese compositeoxides such as LiMn₂O₄, lithium nickel oxides such as LiNiO₂, otheroxides obtained by substituting manganese, nickel and cobalt in theabove oxides partially with other transition metals, orlithium-containing vanadium oxide, etc.); or calcogenides, such asmanganese dioxide, titanium disulfide, molybdenum disulfide, etc.

Anode active materials that may be used in the present invention includethose currently used in anodes for electrochemical devices. Particularexamples of the anode active materials include lithium metal, lithiumalloys, carbon, petroleum coke, activated carbon, graphite or carbonfiber capable of lithium ion intercalation/deintercalation. Other metaloxides capable of lithium intercalation/deintercalation and having apotential vs. Li⁺/Li of less than 2V (for example, TiO₂ or SnO₂) mayalso be used. Particularly, carbonaceous materials, such as graphite,carbon fiber or activated carbon are preferred.

There is no particular limitation in the current collector, as long asthe collector is formed of a highly conductive metal, allows easyattachment of slurry of an electrode active material thereto, and has noreactivity in the drive voltage range of the battery. Non-limitingexamples of a cathode collector include foil formed of aluminum, nickelor a combination thereof. Non-limiting examples of an anode collectorinclude foil formed of copper, gold, nickel, copper alloys or acombination thereof.

Particular examples of the binder that may be used in the presentinvention include polytetrafluoroethylene (PTFE), polyvinylidenefluoride (PVdF), or the like.

There is no particular limitation in the conductive agent, as long asthe conductive agent is an electroconductive material that does notcause a chemical change in the electrochemical device. In general,carbon black, graphite, carbon fibers, carbon nanotubes, metal powder,conductive metal oxide, organic conductive agents may be used.Commercially available conductive agents include acetylene black-basedconductive agents (available from Chevron Chemical Company or Gulf OilCompany), Ketjen Black EC series (available from Armak Company), VulcanXC-72 (available from Cabot Company) and Super P (available from MMMCo.).

As the solvent for forming the slurry, organic solvents, such as NMP(N-methyl pyrrolidone), DMF (dimethyl formamide), acetone or dimethylacetamide, water, etc. may be used. Such solvents may be used alone orin combination. The solvent is used in an amount sufficient fordissolving and dispersing the electrode active material, the binder andthe conductive agent therein, considering the coating thickness of theslurry and the productivity.

Although there is no particular limitation in the separator that may beused in the present invention, a porous separator is preferred, andparticular examples thereof include polypropylene-based,polyethylene-based, and polyolefin-based porous separators.

Further, although there is no particular limitation in the outer shapeof the electrochemical device according to the present invention, theelectrochemical device may have a cylindrical shape using a can, aprismatic shape, a pouch-like shape or a coin-like shape.

Reference will now be made in detail to the preferred embodiments of thepresent invention. It is to be understood that the following examplesare illustrative only and the present invention is not limited thereto.

Example 1

First, 1M LiPF₆ was dissolved into an organic solvent containingethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a ratio of3:7 (v:v, EC:EMC) to provide a solution. Next, 0.5 wt % ofditrimethylolpropane tetraacrylate represented by the following Formula5 and 3.0 wt % of propane sultone were added to the solution asadditives to provide a non-aqueous electrolyte.

LiCoO₂ was used as a cathode active material, and artificial graphitewas used as an anode active material. A bicell type pouch battery wasprovided by using the cathode active material, the anode active materialand the electrolyte obtained as described above.

Example 2

An electrolyte and a battery were provided in the same manner asdescribed in Example 1, except that ethylene sulfite was added insteadof propane sultone.

Example 3

An electrolyte and a battery were provided in the same manner asdescribed in Example 1, except that dipentaerythritol hexaacrylaterepresented by the following Formula 6 was added instead ofditrimethylolpropane tetraacrylate represented by the above Formula 5.

Example 4

An electrolyte and a battery were provided in the same manner asdescribed in Example 1, except that propenyl methanesulfonate was addedinstead of propane sultone.

Comparative Example 1

An electrolyte and a battery were provided in the same manner asdescribed in Example 1, except that propane sultone was not added.

Comparative Example 2

An electrolyte and a battery were provided in the same manner asdescribed in Example 3, except that propane sultone was not added.

Comparative Example 3

An electrolyte and a battery were provided in the same manner asdescribed in Example 1, except that ditrimethylolpropane tetraacrylate(Formula 5) was not added.

Comparative Example 4

An electrolyte and a battery were provided in the same manner asdescribed in Example 2, except that ditrimethylolpropane tetraacrylate(Formula 5) was not added.

Comparative Example 5

An electrolyte and a battery were provided in the same manner asdescribed in Example 4, except that ditrimethylolpropane tetraacrylate(Formula 5) was not added.

Comparative Example 6

An electrolyte and a battery were provided in the same manner asdescribed in Example 1, except that ditrimethylolpropane tetraacrylate(Formula 5) and propane sultone were not added.

Experimental Example 1 Test for Lifespan Characteristics

The pouch batteries according to Examples 1˜4 and Comparative Examples1˜6 were subjected to 200 charge/discharge cycles under 0.5 C. Eachbattery was measured for the capacity maintenance (%) based on theinitial capacity. The following Table 1 shows the results.

Experimental Example 2 Test for Measuring Change in Thickness UnderHigh-Temperature Storage Conditions

The batteries according to Examples 1˜4 and Comparative Examples 1˜6were heated from room temperature to 90° C., and then stored at 90° C.for 4 hours. Next, real-time measurement for a change in the thicknessof each battery was performed while cooling the battery from 90° C. for1 hour. The results are shown in the following Table 1.

TABLE 1 Capacity Increment in maintenance thickness after under 200charge/ high- discharge temperature Additives cycles (%) (mm) Ex. 1Ditrimethylolpropane 87.1 0.45 tetraacrylate 0.5 wt % + Propane sultone3 wt % Ex. 2 Ditrimethylolpropane 85.3 0.62 tetraacrylate 0.5 wt % +Ethylene sulfite 3 wt % Ex. 3 Dipentaerythritol hex- 88.5 0.51 aacrylate0.5 wt % + Propane sultone 3 wt % Ex. 4 Ditrimethylolpropane 82.8 0.68tetraacrylate 0.5 wt % + Propenyl methansulfonate 3 wt % Comp. Ex. 1Ditrimethylolpropane 65.4 2.1 tetraacrylate 0.5 wt % Comp. Ex. 2Dipentaerythritol hex- 67.7 2.4 aacrylate 0.5 wt % Comp. Ex. 3 Propanesultone 3 wt % 68.8 1.8 Comp. Ex. 4 Ethylene sulfite 3 wt % 65.2 1.9Comp. Ex. 5 Propenyl methansulfonate 3 70.5 2.5 wt % Comp. Ex. 6 None52.3 3.4

As can be seen from Table 1, the batteries using the combination of anacrylate compound with a sulfinyl group-containing compound showsignificantly improved lifespan characteristics, as compared to thebatteries using each single compound.

Additionally, the increment in the thickness of a battery is inproportion to the amount of gas generation inside a battery. Like theresults of the test for evaluating lifespan characteristics, thebatteries using the combination of an acrylate compound with a sulfinylgroup-containing compound show a lower increment in the thickness causedby the gas generation under high-temperature storage conditions, ascompared to the batteries using each single compound.

Experimental Example 3 Investigation of SEI Layer Formation on Anode ViaReaction of Additive

The electrolytes according to Examples 1˜4 and Comparative Examples 1˜6were used along with artificial graphite as a cathode and lithium foilas an anode to provide coin type half cells in the conventional manner.Each of the coin type half cells was subjected to three times ofcharge/discharge cycles under 0.2 C at 23° C., each cell wasdisassembled, and then the anode was collected from each cell in adischarged state. The anode was analyzed by DSC (differential scanningcalorimetry) and the peak heat emission temperature was measured. Theresults are shown in the following Table 2. It is generally thought thatthe heat emission peak is the result of the thermal degradation of theSEI film on the surface of the anode.

TABLE 2 Initial heat emission temperature Additives (° C.) Ex. 1Ditrimethylolpropane tetraacrylate 0.5 125 wt % + Propane sultone 3 wt %Ex. 2 Ditrimethylolpropane tetraacrylate 0.5 124 wt % + Ethylene sulfite3 wt % Ex. 3 Dipentaerythritol hexaacrylate 0.5 wt % + 127 Propanesultone 3 wt % Ex. 4 Ditrimethylolpropane tetraacrylate 0.5 126 wt % +Propenyl methansulfonate 3 wt % Comp. Ex. 1 Ditrimethylolpropanetetraacrylate 0.5 123 wt % Comp. Ex. 2 Dipentaerythritol hexaacrylate0.5 122 wt % Comp. Ex. 3 Propane sultone 3 wt % 123 Comp. Ex. 4 Ethylenesulfite 3 wt % 119 Comp. Ex. 5 Propenyl methansulfonate 3 wt % 120 Comp.Ex. 6 None 112

After the experiment, the cells using an acrylate compound incombination with a sulfinyl group-containing compound as electrolyteadditives according to Examples 1˜4, and the cells using each of theabove compounds alone according to Comparative Examples 1˜6 showeddifferent initial heat emission temperatures at the anodes. It can beseen from the above experimental results that the compounds used in theelectrolyte according to the present invention, i.e. both the acrylatecompound and the sulfinyl group-containing compound participate in theformation of the SEI layers on the anode surfaces.

INDUSTRIAL APPLICABILITY

As can be seen from the foregoing, the non-aqueous electrolytecomprising an acrylate compound in combination with a sulfinylgroup-containing compound makes it possible for the acrylate compound toform an SEI layer on the anode and for the sulfinyl group-containingcompound to maximize the effect provided by the acrylate compound.Therefore, the electrochemical device, such as the secondary battery,using the non-aqueous electrolyte can provide improved lifespancharacteristics and thermal safety.

Although several preferred embodiments of the present invention havebeen described for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

The invention claimed is:
 1. An electrochemical device comprising acathode, an anode and a non-aqueous electrolyte solution, wherein: (i)the non-aqueous electrolyte solution comprises: (A) a mixture ofcompounds suitable for producing a solid electrolyte interface (SEI)layer on an electrode, the compounds consisting essentially of: (1) anacrylate compound; and (2) a sulfinyl group-containing compound; (B) anorganic solvent, and; (C) an electrolyte salt; and/or (ii) the cathodeand/or the anode comprises a SEI layer formed partially or totally on asurface thereof, the SEI layer consisting essentially of: (D) a reducedform of the acrylate compound; and (E) a reduced form of the sulfinylgroup-containing compound.
 2. The electrochemical device as claimed inclaim 1, which is a lithium secondary battery.
 3. The electrochemicaldevice as claimed in claim 1, wherein the acrylate compound is selectedfrom the group consisting of tetraethyleneglycol diacrylate,polyethyleneglycol diacrylate (molecular weight 50˜20,000), bisphenol Aethoxylated diacrylate (molecular weight 100˜10,000), 1,4-butanedioldiacrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate,trimethylolpropane ethyoxylate triacrylate, trimethylolpropanepropoxylate triacrylate, ditrimethylolpropane tetraacrylate,pentaerythritol tetraacrylate, pentaerythritol ethoxylate tetraacrylate,dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, andtris[2-(acryloyloxy)ethyl]isocyanurate.
 4. The electrochemical device asclaimed in claim 1, wherein the sulfinyl group-containing compound isselected from the group consisting of sulfites, sulfonates and sultones.